Fiance wants me to take him back after he punched me in the face! Advice?

Im 26, American and have a 5yr old son with my ex fiance, we broke up last year after dating for 6yrs, He is 28 & is Greek but we met when i was studying in Italy, I was head over heels for him and he was very intense with me always by my side holding me. Before my son was born we moved back to the states as i wanted him to be born here, My ex became very possessive, He always wanted to know where i was going, who i was with etc. He has a very short fuse and i know he has the tendency's to be violent as two years ago he was arrested for attacking a bouncer, causing the man to lose 3 teeth, but the guy didn't press charges, We argued alot but despite all of it he always told me how much he loved me and couldn't imagine being without me or our son, He never once showed his violent side to our son. Last July i decided i couldn't expose our son to this kind of life anymore and while my son was with my friends, i broke up with my fiance telling him that he terrified me, although he pleaded with me to stay telling me he loved me etc, As i went to walk away from him, He punched me as hard as he could in the face, The force of it knocked me down. I ended up with a black eye & needed stitches to my cheekbone. I left boston to my hometown with my son, which is NY, I hadn't seen him since we left but since last month he was come by our apartment which i don't know how we found and waits outside my job begging me to talk to him and to give him another chance saying he f*cked up big and cant be with out us, That might have worked on me if i didn't have my son but i need to protect him, He loves his dad and two days ago he seen him & he started to cry saying he misses daddy, When i begged my ex not to upset him and go away he kissed me against my will and put his head level with mine saying its only a matter of time before we are together again, He freaked me out and i feel like he is everywhere i am, I looked for a restraining order but apparently i didn't have enough evidence because i never reported anything previous and that my son has a right to see his father. Any advice on what i should do, alhough i try to not let him see it, Im afraid of him?